CANopen in glass production
Source: CAN Newsletter 3/2007
To manufacture crystal glass, plants with large distances between the processes are necessary. Such a plant consists of a blast furnace, filling stations, and an injection station that revolves. Up to 30 emergency buttons are located along the blast furnace at the respective filling stations. These are distributed over a length of up to 1 km. To achieve the desired results, the pouring of the liquid glass mass must never stop. Also the injection station with revolving head must never be stopped to avoid spillage of the glass liquid. The blast furnace must be kept at a constant operating temperature and may not be switched off. However, it does happen from time to time that an emergency button is being pushed despite the fact that there is no emergency. This may happen involuntarily or maliciously. Due to the above-mentioned reasons, down time would lead to material loss of money. The emergency buttons are not all well within view due to the large physical expanse of the plant. An electrician may therefore have to look for a considerable time to find, which emergency button has been pushed.
- Schematic layout of a blast furnace with CANopen network
Eight emergency controllers were connected via CANopen to the main controller directly. With adequate extension modules almost any number of emergency stop buttons may be connected. Especially in plants that cover a large area and use many of these buttons, CANopen is suitable to reduce the cost of hard wiring. Every emergency controller integrates a CANopen interface. This enables finding out, which emergency button exactly was pushed. It may also be of interest, when and how often each button has been pushed. The controller may also be equipped with a PLC and a human machine interface, both with CANopen interface. Data may thus be registered, documented and displayed without great wiring efforts.
The controller recognizes and saves even very short contact interruptions within emergency buttons (within 2 ms). These may e.g. take place due to corrosion or vibration. The short interruptions are queried via the CANopen network from the PLC. Users may program the time slot for requesting the condition of an emergency button through the PLC themselves. Thus the device in connection with CANopen is also suitable for error diagnosis. The ensuing documentation enables the plant operator to service or exchange the defect device. The configuration of CANopen devices is done via software, e.g. Codesys. Every CANopen device requires a driver with configuration data, which is available from the company.
